Using non-precipitating monospecific antibodies we have studied the conformations of hemoglobin A in solution. Hemoglobin A was purified and isotopically labeled either by carbamoylation with K14 CNO or by reductive alkylation with tritiated borohydride. A specific subpopulation of anti-hemoglobin antibodies has been isolated by affinity chromatography using a synthetic peptide corresponding to alpha (129-141) and has been used in a radio-immunoassay to study conformational changes that occur at the carboxy-terminus of alpha chains during oxygenation. These antibodies which bind with an affinity of 5x10 to the 8th power M-1 to CO-liganded 14(C) hemoglobin increase the oxygen affinity of hemoglobin and, thus, act as a linked function.